An optical sub-assembly is a main part in modern communications technologies, and is likely to fail due to electromagnetic interference from the outside. A conventional optical sub-assembly is generally packaged in a module, and electromagnetic shielding is performed by using a metal housing of the module.
However, with development of technologies and a requirement of costs reduction, currently, some optical sub-assemblies are directly disposed by means of welding on an external printed circuit board (PCB). Due to lack of shielding by a housing of a module, the optical sub-assemblies are subject to electromagnetic interference from the outside of the sub-assemblies. Therefore, a technical problem of “external electromagnetic shielding of an optical sub-assembly” is to be resolved.
In addition, electromagnetic crosstalk always exists between optical components inside an optical sub-assembly, and crosstalk between a transmitter (Tx for short) and a receiver (Rx for short) in a bi-directional optical sub-assembly (BOSA for short) is the most common. The crosstalk includes optical crosstalk and electrical crosstalk. Therefore, a technical problem of “internal electromagnetic shielding of an optical sub-assembly” is to be resolved.
Currently, a main solution in the industry is using a metal shielding case, as shown in FIG. 1. A packaging area and jacks are disposed around a BOSA, and the metal case has pins. The pins are inserted into the jacks on a printed circuit board (PCB for short) during packaging, and are fastened by means of welding. The metal housing needs to be grounded. To prevent electromagnetic leakage, the metal case needs to be firmly welded to be tightly close to supporting parts surrounding the optical sub-assembly, so as to ensure that no crack exists in an exterior of the optical sub-assembly and prevent the electromagnetic leakage. However, the solution has the following disadvantages:
1. An external electromagnetic shielding part of the optical sub-assembly is difficult to disassemble and assemble, and to return for repair.
In a case in which a requirement of shielding performance is strict, welded pins are densely arranged on the metal case. Sometimes, to ensure tight welding, airtight welding needs to be further performed on a seam, which causes a worker to spend a long time in welding and costs a lot. In addition, airtight welding relies heavily on skills of a worker. Effects of welding by different workers or even by a same worker in different time are different. Therefore, there are great risks in welding yield and performance.
Therefore, to prevent electromagnetic leakage, the metal case is difficult to “assemble”, and difficult “assembly” means more difficult “disassemble”. For a metal case that has dense welding joints or on which airtight welding is performed, it is undoubtedly time-consuming and laborious to dismantle the metal case. Existing production experience indicates that such disassembly usually damages the internal optical sub-assembly. However, when the optical sub-assembly is returned for repair, the shielding case needs to be disassembled. Therefore, conventional electromagnetic shielding of the optical sub-assembly implemented by using a metal shielding case is particularly unfavorable to return for repair of the optical sub-assembly.
2. An internal electromagnetic shielding part of the optical sub-assembly is difficult to package and miniaturize.
For the technical problem of “external electromagnetic shielding of an optical sub-assembly”, there is no satisfactory solution in the industry currently. Main solutions are making Rx and Tx signal cables far from each other, using a small metal case for shielding, and the like. All these measures require the optical sub-assembly to have a large enough volume to provide a distance between the signal cables and place the small metal case. Therefore, it is difficult to implement miniaturization of the optical sub-assembly. In addition, packaging a metal case inside a component is rather difficult in techniques because welding is needed.
3. An electromagnetic shielding part of the optical sub-assembly needs to be grounded.
Grounding processing is needed in all existing solutions in the industry in which a metal shielding case is used. For the grounding processing, a ground terminal needs to be specially arranged, which causes difficulties in designing and manufacturing a component and a board, and the component and the board can hardly be used universally or standardized. Because a ground is public, disassembly and assembly affect performance of another component.